Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.47   9.184%   $61.6562   $61.66   $61.65   $61.70  
  Purchase #2 $128.84   13.383%   $146.0827   $146.08   $146.10   $146.10  
  Purchase #3 $95.26   7.271%   $102.1864   $102.19   $102.20   $102.20  
  Purchase #4 $139.65   7.663%   $150.3514   $150.35   $150.35   $150.40  
  Purchase #5 $187.45   8.192%   $202.8059   $202.81   $202.80   $202.80  
  Purchase #6 $223.47   11.840%   $249.9288   $249.93   $249.95   $249.90  
  Purchase #7 $57.62   8.509%   $62.5229   $62.52   $62.50   $62.50  
  7 purchase totals = $888.76       $975.5343   $975.54   $975.55   $975.60